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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

454

D&GRAS

DEGRAS

Genuine degras (natural degras) is a secondary product of the chamoising
of skins. It consists of marine animal oil (especially whale oil), in which
the action of atmospheric oxygen has led to the formation of resinous
hydroxy-acids (Degragene), emulsified with water and containing small
proportions of mineral substances (soda, lime, sulphates) and organic
residues (hide, membranous fragments) resulting from the method of
preparation.

This product forms a fairly dense, almost pasty, yellow or orange liquid,
which has a special odour recalling that of fish oil and remains homogeneous
even on long standing.

Artificial degras is obtained by mixing natural degras with fish, mineral
or resin oil, vaseline, wool fat, tallow, etc., or by artificial oxidation of fish
oils, followed by emulsification with water and sometimes by addition of
the other extraneous substances mentioned above.

Artificial degras is also a yellow or orange dense liquid, which is usually
more liquid than the natural product and has a peculiar fish oil odour ;
on long standing, it tends to divide into two layers, the water settling to
the bottom.

Analysis of degras includes various determinations and tests to serve
as a guide in ascertaining if it is a natural or artificial product, if it is pure,
that is, based solely on fish oils, or if it is mixed with tallow, wool fat, mineral
oils, vaseline or resin oils, these being the most frequent additions to
degras.

The principal determinations are as follows :

1.  Water.10 grams of the degras are  placed in a porcelain dish
previously heated to redness with about 10 grams of coarse quartz sand
and tared ; the fat is mixed well with the sand and the dish and contents
dried at 120 until of constant weight (4-5 hours).   The loss in weight
gives the water.

2.  Non-fatty Substances  (Organic Residues).20 grams   of the
degras   are dried  in an oven at 120 OF even over a direct flame, the
liquid being stirred with a thermometer and care taken that its temperature
does not exceed 105; the dried product is dissolved in petroleum ether
and the solution filtered through a tared filter, the insoluble mattei being
washed with petroleum ether and then with a little ether or benzene and
alcohol, dried at 100 and weighed.

This insoluble matter consists principally of epidermis and hide residues
readily recognisable with a lens or microscope, together with a few other
impurities.

On the other hand, evaporation of the petroleum solution and weighing
of the residue dried at 105 gives the total fat; the latter is used for the
determinations indicated under 4 (below),

3.  Ash.10 grams of the  degras are carefully heated in a platinum
dish over a naked flame until copious fumes are emitted, the dish being
then heated more strongly on a sand-bath and finally in a muffle at a dull
red heat.   The ash is mainly alkali and alkaline-earthy sulphates ;   it is fat.